This invention relates a method for the froth flotation of coal and, more particularly, to the use of a condensation product of an alkanolamine and naphthenic acid as a conditioner for the flotation of coal.
Combustible carbonaceous solid material ("coal") is inherently found in deposits containing non-combustible mineral matter. Although large fragments of the non-combustible materials can be removed by screening or conventional gravity concentration techniques such as centrifugation, froth flotation is more commonly employed to remove the coal from the finer non-combustible materials. In froth flotation, a frother such as methyl isobutyl carbinol. In the flotation process, it is desirable to recover as much coal as possible while effecting the recovery in a selective manner, i.e., minimizing the amounts of undersirable material or ash in the froth. Unfortunately, many coals, e.g., coals in which the surface has been at least partially oxidized such as sub-bituminous and anthracite coals, are difficult to float. This results in an undesirable loss of significant amounts of combustible material in the tail from the flotation.
Increases in the amounts of this so-called "hard-to-float" coal recovered in the froth can be improved by increasing the concentration of the oil-type collector employed in the flotation process. Unfortunately, acceptable recovery can often be effected using such high amounts of the oil-type collector that significant amounts of the non-combustible matter are floated with the coal. Sun suggests in Trans. AIME, 199:396-401 (1954), that fatty amines can be utilized as co-collectors in the flotation of oxidized coals to effect enhanced recovery. However, even these amine collectors float substantial amounts of ash along with the coal and effect only partial recovery of combustible material.
A variety of other materials have been suggested for use into beneficiate coal in a froth flotation process. Such materials include the condensation product of a fatty acid or fatty acid ester with the reaction product of a polyalkylenepolyamine and an alkylene oxide (U.S. Pat. No. 4,305,815); the condensation product of an alkanolamine and a fatty acid or fatty acid ester (U.S. Pat. No. 4,474,619) and the reaction product of the condensation product of diethanolamine and a C.sub.10-24 fatty acid with a C.sub.1-4 monocarboxylic acid (U.S. Pat. No. 4,330,339). These materials can be effectively employed in the flotation of coal and are capable of the selective recovery of coal over ash at excellent rates of recovery. However, the fatty acid component of the conditioner is subject to variation in cost. In addition, further improvements in the selectivity of the froth flotation process or in the rate of coal recovery are always desirable.
Therefore, it is desirable to provide an alternative method for conditioning or beneficiating coal which gives equivalent or better performance than existing methods.